How to get my IP address programmatically on iOS/macOS?

Question

I would like to obtain my iPad's IP address programmatically. How can I query the networking subsystem to find out what my IPv4 (and IPv6) addresses are?

PS: Can I disable IPv6 somehow?

Answer 1

The following code finds all IPv4 and IPv6 addresses on an iOS or OSX device. The first getIPAddress method acts more or less as the older code in this answer: you can prefer either one or the other type address, and it always prefers WIFI over cellular (obviously you could change this).

More interestingly it can return a dictionary of all addresses found, skipping addresses for not up interfaces, or addresses associated with loopback. The previous code as well as other solutions on this topic will not properly decode IPv6 (inet_ntoa cannot deal with them). This was pointed out to me by Jens Alfke on an Apple forum - the proper function to use is inet_ntop (look at the man page, and or refer to this inet_ntop article also provided by Jens.

The dictionary keys have the form "interface" "/" "ipv4 or ipv6".

#include <ifaddrs.h>
#include <arpa/inet.h>
#include <net/if.h>

#define IOS_CELLULAR    @"pdp_ip0"
#define IOS_WIFI        @"en0"
//#define IOS_VPN       @"utun0"
#define IP_ADDR_IPv4    @"ipv4"
#define IP_ADDR_IPv6    @"ipv6"

- (NSString *)getIPAddress:(BOOL)preferIPv4
{
    NSArray *searchArray = preferIPv4 ?
                            @[ /*IOS_VPN @"/" IP_ADDR_IPv4, IOS_VPN @"/" IP_ADDR_IPv6,*/ IOS_WIFI @"/" IP_ADDR_IPv4, IOS_WIFI @"/" IP_ADDR_IPv6, IOS_CELLULAR @"/" IP_ADDR_IPv4, IOS_CELLULAR @"/" IP_ADDR_IPv6 ] :
                            @[ /*IOS_VPN @"/" IP_ADDR_IPv6, IOS_VPN @"/" IP_ADDR_IPv4,*/ IOS_WIFI @"/" IP_ADDR_IPv6, IOS_WIFI @"/" IP_ADDR_IPv4, IOS_CELLULAR @"/" IP_ADDR_IPv6, IOS_CELLULAR @"/" IP_ADDR_IPv4 ] ;

    NSDictionary *addresses = [self getIPAddresses];
    NSLog(@"addresses: %@", addresses);

    __block NSString *address;
    [searchArray enumerateObjectsUsingBlock:^(NSString *key, NSUInteger idx, BOOL *stop)
        {
            address = addresses[key];
            if(address) *stop = YES;
        } ];
    return address ? address : @"0.0.0.0";
}

- (NSDictionary *)getIPAddresses
{
    NSMutableDictionary *addresses = [NSMutableDictionary dictionaryWithCapacity:8];

    // retrieve the current interfaces - returns 0 on success
    struct ifaddrs *interfaces;
    if(!getifaddrs(&interfaces)) {
        // Loop through linked list of interfaces
        struct ifaddrs *interface;
        for(interface=interfaces; interface; interface=interface->ifa_next) {
            if(!(interface->ifa_flags & IFF_UP) /* || (interface->ifa_flags & IFF_LOOPBACK) */ ) {
                continue; // deeply nested code harder to read
            }
            const struct sockaddr_in *addr = (const struct sockaddr_in*)interface->ifa_addr;
            char addrBuf[ MAX(INET_ADDRSTRLEN, INET6_ADDRSTRLEN) ];
            if(addr && (addr->sin_family==AF_INET || addr->sin_family==AF_INET6)) {
                NSString *name = [NSString stringWithUTF8String:interface->ifa_name];
                NSString *type;
                if(addr->sin_family == AF_INET) {
                    if(inet_ntop(AF_INET, &addr->sin_addr, addrBuf, INET_ADDRSTRLEN)) {
                        type = IP_ADDR_IPv4;
                    }
                } else {
                    const struct sockaddr_in6 *addr6 = (const struct sockaddr_in6*)interface->ifa_addr;
                    if(inet_ntop(AF_INET6, &addr6->sin6_addr, addrBuf, INET6_ADDRSTRLEN)) {
                        type = IP_ADDR_IPv6;
                    }
                }
                if(type) {
                    NSString *key = [NSString stringWithFormat:@"%@/%@", name, type];
                    addresses[key] = [NSString stringWithUTF8String:addrBuf];
                }
            }
        }
        // Free memory
        freeifaddrs(interfaces);
    }
    return [addresses count] ? addresses : nil;
}

EDIT1: Code updated on May 16, 2014 (bug pointed out by lhunath, see comments). Loopback addresses now returned, but its easy for you to uncomment the test to exclude them yourself.

EDIT2: (by some unknown person): Improved further March 13, 2015: In case the user uses a VPN (regardless over WiFi or Cellular), the previous code would have failed. Now, it works even with VPN connections. VPN connections are given precedence over WiFi and Cell because that's how the device handles it. This should even work for Macs as the VPN connection on a Mac is also using IF utun0 but not tested.

EDIT3: (9/8/2016) Given the problems experienced by @Qiulang (see comments) with the VPN code (which someone else added), I've commented it out. If anyone knows definitively how to specify a user VPN please chime in with a comment.